1. Field of the Invention
The present invention is related to the field of electronic fuel control systems for providing intermittent pulses of fuel to a power producing engine. More particularly, the present invention is related to that portion of the above noted field in which the injection pulses are generated in a time period during which a controlled voltage maintains a selected relationship with respect to a selected threshold value and in which the varying engine operating conditions are used to alter the state of the voltage being examined and/or the level of the selected threshold value. More particularly, the present invention is related to a system by which the value which the injection controlling examined portion of the controlled voltage may originate at is controllably varied as a function of substantially instantaneous engine rpm values.
2. Description of the Prior Art
It is well known in the prior art that the fuel requirement for an engine operating at constant load may vary as a function of the rpm value of the engine. In prior electronic fuel control systems, the rpm corrections have been generally provided by taking the average speed of the engine for a period of time preceding the instantaneous calculation in question and by altering the voltage used to excite one or more of the engine operating parameter sensors.
This approach has presented two difficulties. Firstly, by taking an average of the engine speed over a history of prior events, however brief, the response to changes in engine rpm is slow. Secondly, by applying a variation in the exciting voltage to one or more of the engine parameter sensors, an additional delay has been induced as a result of the inherent response delays in the sensor or sensors so excited. For instance, it has normally been the case to vary the excitation voltage for the intake manifold air pressure sensor. Such a sensor has an internal time delay due to the electrical and mechanical characteristics with which it is designed. Thusly, by the time the information of a change in engine speed is available to affect a change in the amount of fuel delivered to the engine, the engine may be operating under a speed condition which is inappropriate for the amount of fuel being provided by the fuel delivery system at that moment. It is thus an object of the present invention to provide a means for examining the engine rpm on a current, or substantially instantaneous, basis so as to provide the proper quantities of fuel to the engine for each cycle of its operation.
With the advent of fuel delivery computing techniques which rely principally on the excursion of a selected voltage through a selected threshold value it has been determined that an rpm correction may be provided by varying one of the two extreme values which the selected voltage may obtain. That is, for injection systems which provide fuel while a selected voltage is below a reference value, it is possible to vary the value at which that voltage may be initiated so as to controllably vary its total time below the threshold value. My co-pending commonly assigned patent application Ser. No. 219,275 filed January 20, 1972, hereby expressly incorporated herein by reference entitled "Circuit for Providing Electronic Full-Load Enrichment Fuel Compensation in an Electronic Fuel Control System" illustrates a system in which a controlled voltage waveshape is generated having a first shaped portion which generates a correction factor and a second shaped portion following immediately thereon to generate the fuel controlling pulse. The correction factor is provided by controllably varying the initial or starting value of the second shaped portion which in turn varies the time required for the second shaped portion to reach a threshold value. This correction factor is used to provide rpm correction. However, the circuitry of my prior case is capable of providing rpm correction factors on a basis of whether or not engine speed is above or below one selected rpm value. It is now known that rpm correction factors are required as a function of existing speed conditions and the determination of only one rpm value is insufficient. With the circuitry of my prior case, provision of greater detailed rpm information is difficult.
This difficulty arises from the inability of the computing techniques normally used in electronic fuel control systems to identify any particular engine rpm value by means other than integration techniques. Integration techniques provide at best an identification of an engine rpm one cycle after that rpm value is desired and at worst an averaging technique which is the average of rpm values over several past cycles of rpm. For the greatest accuracy of fuel delivery, it is necessary that the rpm information be as current as possible. It is therefore an object of the present invention to provide a means of generating rpm information and for updating this information each injection time period.
In order to match the manufacturing, cost, and accuracy benefits derived from a fuel control system as described in my above-noted co-pending application it is a further object of the present invention to provide circuitry capable of generating rpm information which is completely compatible with the electronics of my prior co-pending application.
In view of the fact that the speed of electronic devices and electronic computing techniques greatly exceeds the speed of operation of an internal combustion engine, it is well within the state-of-the-art to examine the time interval between successive triggering events and to compute therefrom the speed of the engine to generate rpm information which is sufficiently current to meet the general accuracy levels obtained by the present invention. However, by waiting until the occurrence of the next succeeding engine event to generate speed information would require a system of additional electronics to compute the rpm information and to apply that factor to the injection command signaling portion of the system for instance as illustrated and claimed in my above-mentioned co-pending application. It is therefore a still further object of the present invention to generate rpm information during the interval between successive triggering events which is available prior to the occurrence of the succeeding triggering event. As used herein "triggering event" is intended to mean the signal which is used to synchronize the fuel control system to selected angles of engine crank shaft rotation and also the condition of engine operation which gives rise to the signal.
I have determined that computation or generation of exact speed information per se is not necessary in order to achieve the objectives of the present invention and, in fact, the present invention provides suitable information in a form which is much more compatible with my aforementioned application and which is much less expensive to implement in circuit form than would be the electronics necessary to generate information of precise engine rpm. It is therefore an object of the present invention to provide circuitry for generating an rpm information signal which signal is being generated in the interval between successive triggering events without direct input of past triggering events and which does not rely upon the next succeeding triggering event for computation.